1. Field of the Invention
This invention relates to a microprogram controlled processor in which an overwritable memory having stored micro-code is provided within the processor.
2. Prior Art
In a microprogram controlled processor a control memory 1 having stored micro-code is accommodated inside the processor 2, as shown in FIG. 1. The processor 2 interprets and executes the user program that has been loaded into an external memory 3 in accordance with the micro-code program stored in the control memory 1.
The control memory typically included in the processor is usually of the read-only kind containing preprogrammed micro-code and is typically built into the processor originally.
There is also known a method with a view to high-speed execution of the user program in which the control memory included in the processor is adapted to be read out or written into externally, so that the user program can be directly loaded into the control memory for execution without requiring the external memory.
Meanwhile, in implementing a calculation model, such as a function-type model, an object-oriented model, or some other higher level calculation tool, on such a microprogram controlled processor, an execution model made up of executable units forming the program in a particular language or a so-called framework is required.
The architecture of the present-day electronic computer is the so-called von Neumann architecture. That is, underlying the present-day computer architecture are, the data, storage locations for the data, the processor, and the data processing taking place in the processor. For realizing the execution model on such architecture, not only must the processing indicated on the execution model made up of the executable units forming the program be performed by the processor but also the memory supervision or device supervision must be handled by the processor.
While the execution model is determined by the particular calculations to be performed, the system description of, for example, memory supervision, device supervision, library, scheduler, file system or input/output required for implementing the execution model is determined by the particular hardware architecture, as represented for example in FIG. 2. This system description includes processing that cannot be seen directly from the execution model, such as secondary memory supervisions supervision of the calculation process, or allocation of the processor or CPU to the various processes. The result is that compatibility between the execution model and the hardware architecture has been improved in general.
For example, assuming in the system shown in FIG. 1 that a data base A and a data base B are stored in the outside memory 3, and that it is to be determined whether the data base A and the data base B comprise the same data base, the processor 2 sequentially reads and compares the two data bases A and B, and at the same time controls or supervises the memory, main storage device or secondary storage device, in order to render a judgement on whether the data base A is the same as the data base B.
With such architecture, because the system description based on the hardware architecture is not necessarily concise, the actual system operation cannot be easily predicted when implementing the execution model, or when making a system description, or when programming the execution model. The result is that an unexpected hindrance is apt to be encountered, for example, at the time of memory accessing, because other tasks are being performed by the processor and memory access is not immediately available.
Although the use of dedicated machines or functional memories may be envisaged to improve the compatibility between the execution model and the system architecture, a method based on framing that will give fundamentals for calculation on a large number of execution models would be desirable for realizing a universal architecture.
Meanwhile, with a microprogram controlled processor a control memory that permits reading and writing from outside may be included in the processor to speed up execution of the user program. Nevertheless, a large sized program cannot be executed immediately because the necessarily larger storage capacity of the control memory cannot be realized. Thus, when executing a large size program or executing a plurality of programs time-divisionally it becomes necessary to perform external program switching, the result of which is that the execution efficiency may be drastically lowered.